1. Field of the Invention
The invention relates generally to wireless communication systems and more particularly to burst transmissions in a wireless system.
2. Description of Related Art
Wireless communication systems have been developed to allow transmission of information signals between an originating location and a destination location. Both analog (first generation) and digital (second generation) systems have been used to transmit such information signals over communication channels linking the source and destination locations. Digital methods tend to afford several advantages relative to analog techniques, including, e.g., improved immunity to channel noise and interference, increased capacity, and improved security of communication through the use of encryption.
First-generation analog and second-generation digital systems have been designed to support voice communication with limited data communication capabilities. Third-generation (3G) wireless systems, using wide-band multiple access technologies such as CDMA, will effectively handle a large variety of services, such as voice, video, data and imaging. Among the features to be supported by third-generation systems are the transmission of high-speed data between a mobile terminal and a land-line network. High-speed data communications are often characterized by a short transmission xe2x80x9cburstxe2x80x9d at a high data transmission rate, followed by some longer period of little or no transmission activity from the data source. To accommodate the bursty nature of such high-speed data services in third-generation systems, it is necessary for the communications system to assign a large bandwidth segment (corresponding to the high data rate) for the duration of the data burst from time to time.
With the ability of the third generation systems (3G) to handle such bursty high-speed data transmission, throughput and delay for users can be advantageously improved. However, because of the large amount of instantaneous bandwidth required for transmission of a burst of high-speed data, the management of such bursts, and particularly the allocation of power and system resources thereto, must be handled with care to avoid unwarranted interference with other services using the same frequency allocation. Consequently, system designers need to deal with many issues in setting efficient data rates for different types of communications via a wireless link, including appropriate allocation of system resources for the bursts of data experienced with high-speed data service.
There is a continuing need to increase the performance of communication systems by accommodating a variety of users with different data rates. In particular, there is a need to maintain transmission quality by preventing power overloading and excessive interference problems. There is a corollary need for a mechanism that improves or increases the system throughput and data rates of individual users, particularly for high-speed data, accessing a wireless communications system.
With regard to the construction and design of 3G wireless communication systems, high-speed data services must be accommodated into the wireless communication systems while maintaining spectral efficiency in the radio transmission. To achieve such results, a packet transmission mode has been introduced due to the bursty nature of the data communications. The packet transmission mode involves a burst control function which, upon receiving a request for data burst transmission, allocates the radio resources (including burst duration and burst data rate) for each single burst transmission.
One major goal of the burst control function is to insure that each burst transmission will not create excessive (intolerable) interference which may jam or otherwise negatively affect the entire system. The resource assignment for the burst may not be proper, as recognized some time after the start of the burst. Thus, premature termination of the burst may be necessary in the case where severe jamming interference arises unexpectedly. Furthermore, if the burst transmission is the reverse link, from the mobile wireless unit to the base station, this may involve a message between the base station and terminal and may cause some delay in the critical action.
The successive high-speed data services in 3G systems rely heavily on the burst control function. All wireless communication systems require frequency re-use to increase capacity. With the introduction of high-speed packet data services such as IS-95B and 3GIS-95, interference variation becomes more severe than in the case of voice only services. For voice only services, code channels are assigned to various users and every user transmits at roughly the same data rate. Some users encounter severe fading conditions and may need more power (which in turn creates more interference) in order to maintain the quality of the link between the mobile wireless unit and the base station. On the other hand, some others might be in benign conditions and may cause very little interference to others. Since the users are randomly located, the fading conditions for individual users are also random and thus CDMA systems take advantage of an averaging effect on interference.
However, the scenarios for high-speed data services are different. First, a single user can be assigned a large chunk of equivalent code channels for a short interval to serve the user""s bursty data transmission need. If this assigned user happens to encounter a severe fading in the middle of the burst transmission, the associated power with the user will need to be boosted up to maintain call quality. This increase in power might further present excessive interference to all other users due to the high data rate to which it has been assigned. Also, the above-mentioned averaging effect among users is missing because a large portion of radio resources are assigned to a single user in 3G systems and this causes an equivalently higher xe2x80x9cpeak-to-averagingxe2x80x9d interference pattern.
A second scenario involves the mobility of the wireless unit. The assigned high-speed data user may travel at a certain speed. Once it enters a handoff zone, handing off communication of the mobile wireless unit from one base station to another, the interference pattern changes significantly. The new and/or old base station may not have enough radio resources or this high-speed data user may jam other users within the new base station coverage areas.
In short, the aforementioned scenarios present needs to accurately estimate a mobile wireless unit""s fading conditions and interference problems that it may cause for base stations and allocation of radio resources in burst assignments. Further, a need is created to perform strict control on the burst transmission such that interference generated by this high rate user is tolerable to other users. In practical operation, the estimation of the wireless mobile units fading and interference may not be accurate enough and the control of the interference may not be guaranteed especially when the wireless mobile unit is into a transition (add or drop) of soft handoff between base stations. Accordingly, a need exists to perform premature termination of burst transmission, in order to insure control of interference, if significant instantaneous interference rise occurs. If premature termination of burst transmission is to occur by sending a message between the mobile wireless unit and the base station, this message for termination must be transmitted quickly because the delay of action might cause significant degradation for other users on the system.
In order to effectively terminate a burst transmission in a wireless system, a method and apparatus has been developed which determines whether or not a burst transmission from a wireless unit to a base station should be terminated by evaluating at least one criterion related to the operation of the wireless system. Once it is determined that a burst transmission should be terminated, the transmission is terminated by lowering signal-to-interference ratio (SIR) by a predetermined amount. By lowering this target SIR, power control bits transmitted from the base station to the wireless unit instruct an extreme decrease in power of the burst transmission and quickly act to effectively terminate the burst transmission.